Circuit for tracking and maintaining drive of actuator/mass at resonance

Abstract

A drive circuit (10) for driving an actuator/mass (A) at its natural resonance and for maintaining the instantaneous output signal of the mass at a predetermined constant value over a wide range of dynamically changing resonant frequencies, is disclosed. Current sensing circuitry (C) detects an instantanous current passing through the actuator/mass (A). A compensation circuit (D) modifies the instantaneous sensed circuit signal to compensate for dynamically changing physical parameters of the actuator mass and for phase irregularities introduced into the sensed signal when the mass oscillates near its natural resonance. Automatic gain control circuitry (E) alters the actuator drive signal to maintain amplitude of the mass oscillation at a predetermined constant value. A drive circuit (B) performs the actual drive function in response to the feedback signal received from the automatic gain control and compensation circuitry.

What is claimed is: 
     
       1. Drive circuit apparatus for driving an actuator/mass at its natural resonance to maintain the instantaneous output signal of the actuator/mass at a predetermined constant value over a wide range of dynamically changing resonant frequencies, comprising: (a) an actuator/mass having a mass suitably mounted for oscillatory motion in response to activation by an impressed drive signal, said actuator/mass producing an oscillatory actuator output signal having parameters related to both the drive signal and the resonance of said actuator/mass;   (b) sense means operatively connected to said actuator/mass for directly sensing said actuator output signal and for providing a sensed signal in response thereto;   (c) compensation circuit means connected to receive said drive signal and said sensed signal for removing from said sensed signal those said parameters related to the drive signal, thereby leaving those parameters related only to the resonance of said actuator/mass, and for producing a compensated sensed signal responsive thereto; wherein the phase of said compensated sensed signal is a function of the simultaneous change in the natural resonant frequency of the actuator/mass, and wherein the amplitude of said compensated sensed signal is a function of the instantaneous amplitude of oscillatory motion of the actuator/mass;   (d) automatic gain control means operatively connected to receive said compensated sensed signal for providing in response thereto a feedback signal having the same phase as said compensated sensed signal, having frequency equal to the natural resonant frequency of the actuator/mass and having an amplitude proportional to the difference in amplitude of said compensated sensed signal from a predetermined absolute constant value; and   (e) amplifier drive means operatively connected with said automatic gain control means, with said actuator/mass and with said compensation circuit means for producing said drive signal in response to said feedback signal for driving said actuator/mass and said compensation circuit means; whereby said actuator/mass is driven at its instantaneous natural resonant frequency so as to maintain the amplitude of oscillatory motion of the actuator/mass within predetermined limits of said absolute contant value.   
     
     
       2. Drive circuit apparatus as recited in claim 1, wherein said compensation circuit means comprises: (a) a compensation actuator/mass of like configuration and material as said actuator/mass, but having significantly different resonance from that of said actuator/mass, said compensation actuator/mass being connected to receive said drive signal and producing an oscillatory compensation output signal in response to said drive signal; and   (b) signal processing means operatively connected to receive said sensed signal and said compensation output signal for producing in response thereto said compensated sensed signal.   
     
     
       3. Drive circuit apparatus as recited in claim 2, wherein said signal processing means includes an amplifier circuit for combining said sensed signal and said compensation output signal. 
     
     
       4. Drive circuit apparatus as recited in claim 3, wherein said amplifier circuit comprises a differential amplifier. 
     
     
       5. Drive circuit apparatus as recited in claim 4, wherein said actuator/mass and said compensation actuator/mass include piezoelectric blender elements, and wherein said differential amplifier subtracts said compensation output signal from said actuator output signal. 
     
     
       6. Drive circuit apparatus as recited in claim 2, wherein said actuator/mass and said compensation actuator/mass include piezoelectric bender elements. 
     
     
       7. Drive circuit apparatus as recited in claim 1, wherein said actuator/mass includes a piezoelectric blender element. 
     
     
       8. Drive circuit apparatus as recited in claim 1, wherein said actuator/mass comprises a piezoelectric bender element, and wherein said amplifier drive means comprises a complimentary amplifier circuit. 
     
     
       9. Drive circuit apparatus as recited in claim 1, wherein said automatic gain control means comprises: (a) voltage reference circuit means for providing a constant voltage reference signal;   (b) detector circuit means operatively connected to receive said compensated sensed signal for producing a detected output signal having a voltage level proportional to the peak value of said actuator output signal;   (c) integrator circuit means operatively connected to receive said voltage reference signal and said detected output signal for providing an integrated output signal proportional to the integral of the difference of said detected output signal and said reference voltage signal; and   (d) a gain control circuit operatively connected to receive said integrated output signal for varying the amplitude of said compensated sensed signal in response thereto, thereby controlling the system loop gain; whereby the varied compensated sensed signal comprises said feedback signal.   
     
     
       10. Drive circuit apparatus as recited in claim 1, wherein said compensation circuit means comprises: (a) a circuit model being connected to receive and being driven by said drive signal and having electrical parameters matched to those of said actuator/mass when driven by said drive signal, but having negligible resonance with respect to that of said actuator/mass, said circuit model being operative to produce an oscillatory compensation output signal in response to said drive signal; and   (b) signal processing means operatively connected to receive said sensed signal and said compensation output signal for producing in response thereto said compensated sensed signal.   
     
     
       11. The combination with an actuator/mass of the type that produces oscillatory motion in response to an impressed voltage and an output voltage in response to an impressed force, of a drive circuit comprising: (a) drive amplifier means for directly driving the actuator/mass by applying a drive voltage to the actuator/mass in response to a feedback signal, whereby the actuator mass produces an actuator output signal having both physical and electrical parameters;   (b) sensor means connected to directly sense said actuator output signal for producing a sensed output signal in response thereto;   (c) feedback circuit means operatively connected to receive said sensed output signal for producing said feedback signal in response thereto; wherein said feedback signal has phase parameters suitable for maintaining drive of the actuator/mass at its natural resonance, and amplitude parameters suitable for maintaining the amplitude of said actuator output signal at a constant predetermined level over a broad range of dynamically changing natural resonant frequencies; said feedback circuit means including compensation circuit means connected to receive said sensed output signal for altering the phase characteristics of said sensed output signal to respond to dynamically changing physical properties of said actuator/mass, wherein said compensation circuit means comprises: (i) a compensation actuator/mass operatively connected to receive said drive voltage and having electrical properties except for resonance similar to those of said actuator/mass; and   (ii) comparator means for comparing the responses of said actuator/mass and said compensation actuator/mass when energized by said drive voltage, for producing said altered sensed signal in response thereto; and     (d) means operatively connecting said feedback circuit means with said drive amplifier means, for applying said feedback signal to said drive amplifier means; whereby a closed-loop drive circuit is established.   
     
     
       12. The apparatus as recited in claim 11, wherein said sensor means includes a current detector operatively connected with said actuator/mass for detecting the current flow signal through said actuator means. 
     
     
       13. The apparatus as recited in claim 11, wherein said feedback circuit means includes automatic gain control means connected to receive said sensed output signal and for altering the amplitude of said sensed output signal to identically offset the amplitude variations of the sensed output signal from a predetermined absolute constant value. 
     
     
       14. The combination with an actuator/mass of the type that produces oscillatory motion in response to an impressed voltage and an output voltage in response to an impressed force, of a drive circuit comprising: (a) drive amplifier means for directly driving the actuator/mass by applying a drive voltage to the actuator/mass in response to a feedback signal, whereby the actuator/mass produces an actuator output signal having both physical and electrical parameters;   (b) sensor means connected to directly sense said actuator output signal for producing a sensed output signal in response thereto;   (c) feedback circuit means operatively connected to receive said sensed output signal for producing said feedback signal in response thereto; wherein said feedback signal has phase parameters suitable for maintaining drive of the actuator/mass at its natural resonance, and amplitude parameters suitable for maintaining the amplitude of said actuator output signal at a constant predetermined level over a broad range of dynamically changing natural resonant frequencies; wherein said feedback circuit means includes compensation circuit means and automatic gain control means for respectively altering the phase and amplitude parameters of said sensed output signal in response to the dynamically changing phase and amplitude parameters respectively of said actuator/mass; and wherein said automatic gain control means comprises: (i) voltage reference circuit means for providing a constant voltage reference signal;   (ii) detector circuit means operatively connected to receive said phase altered sensed output signal for producing a detected output signal having a voltage level proportional to the peak value of said actuator output signal;   (iii) integrator circuit means operatively connected to receive said voltage reference signal and said detected output signal for providing an integrated output signal proportional to the integral of the difference of said detected output signal and said reference voltage; and   (iv) a gain control circuit operatively connected to receive said integrated output signal for varying the amplitude of said phase altered sensed signal in response thereto, thereby controlling the system loop gain; whereby the phase altered and amplitude varied sensed signal comprises the feedback signal.     
     
     
       15. The apparatus as recited in claim 14, wherein the voltage reference circuit means includes a zener diode circuit for establishing said constant voltage reference signal. 
     
     
       16. An actuator/mass drive circuit for continuously driving an actuator/mass having dynamically changing resonance, at its resonant frequency so as to maintain a constant amplitude signal therefrom, comprising: (a) a drive circuit responsive to a feedback signal for producing a drive signal to drive said actuator/mass at its natural resonance, wherein said driven actuator/mass produces an oscillatory actuator output signal including parameters related to both drive signal and the resonance of said actuator/mass;   (b) feedback circuit means connected to receive said actuator output signal and being responsive thereto for producing said feedback signal, said feedback circuit means including compensation circuit means for removing from said actuator output signal those said parameters related to said drive signal thereby leaving only those parameters relating to the resonance of said actuator/mass; wherein said feedback signal has phase parameters suitable for maintaining stable drive of said actuator/mass at its natural resonance, and amplitude parameters suitable for maintaining the amplitude of said actuator output signal at a constant predetermined level over a broad range of dynamically changing natural resonant frequencies; wherein said feedback circuit means does not include or depend on any oscillator sources other than said oscillatory actuation output signal to produce said feedback signal; and   (c) means operatively connecting said feedback circuit means with said drive circuit for applying said feedback signal to said drive circuit, whereby a closed-loop self-generating drive circuit is established.   
     
     
       17. The apparatus as recited in claim 16, wherein said drive circuit is operative to maintain the drive of said actuator/mass at its natural resonance over a range of resonant frequencies differing by at least a 10 to 1 ratio. 
     
     
       18. The apparatus as recited in claim 16, wherein said drive circuit is operative to maintain the drive of said actuator/mass at its natural resonance over a range of resonant frequencies differing by at least a 100 to 1 ratio.